全文获取类型
收费全文 | 33937篇 |
免费 | 15912篇 |
国内免费 | 145篇 |
出版年
2024年 | 14篇 |
2023年 | 46篇 |
2022年 | 241篇 |
2021年 | 577篇 |
2020年 | 2313篇 |
2019年 | 3855篇 |
2018年 | 4011篇 |
2017年 | 4232篇 |
2016年 | 4359篇 |
2015年 | 4472篇 |
2014年 | 4174篇 |
2013年 | 4633篇 |
2012年 | 2576篇 |
2011年 | 2226篇 |
2010年 | 3453篇 |
2009年 | 2170篇 |
2008年 | 1246篇 |
2007年 | 723篇 |
2006年 | 717篇 |
2005年 | 679篇 |
2004年 | 599篇 |
2003年 | 534篇 |
2002年 | 495篇 |
2001年 | 413篇 |
2000年 | 342篇 |
1999年 | 276篇 |
1998年 | 62篇 |
1997年 | 54篇 |
1996年 | 48篇 |
1995年 | 44篇 |
1994年 | 44篇 |
1993年 | 33篇 |
1992年 | 48篇 |
1991年 | 40篇 |
1990年 | 24篇 |
1989年 | 27篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 13篇 |
1985年 | 7篇 |
1984年 | 11篇 |
1982年 | 8篇 |
1976年 | 10篇 |
1974年 | 10篇 |
1973年 | 7篇 |
1972年 | 6篇 |
1969年 | 10篇 |
1967年 | 11篇 |
1966年 | 7篇 |
1965年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
121.
Kenji Kato Su-wan Oh Hiroyuki Yamamoto Takayuki Hanazato Ikuko Yasuda Akira Otuki Masayuki Takahashi 《Ecological Research》1992,7(3):267-276
In order to understand the control mechanisms of a large, stable bacterial standing stock, enclosure experiments were conducted
in a eutrophic lake, where both bacterial productivity and grazing pressure were very high. Total bacterial number in the
different enclosures ranged from 1.2 to 2.7×107 cells mL−1 throughout the experiment. The average bacterial cell production rate estimated from a grazer eliminating experiment was
6.3×105 cells mL−1 h−1. Difference in the bacterial cell production rate between shaded and unshaded enclosures was not apparent. Bacteria showed
a reduction in standing stock of only about 25–30% even after the supply of light was cut to 1%. Bacteria in the shaded enclosures
then recovered their production rate in the first 12 days of perturbation. Grazing pressure in the shaded enclosures was not
less than that for the control. Thus, it was considered a control mechanism of bacterial stable standing stock that the bacteria
shifted their organic substrate from extracellular dissolved organic carbon freshly released from phytoplankton to that already
stocked in the water column, though it is not known whether the dominant bacteria were the same. 相似文献
122.
The possession of a respiration-dependent primary sodium pump and the requirement of Na for growth were investigated in bacterial isolates from marine environments. The bacteria in which NADH oxidase specifically required Na for maximum activity were believed to possess a primary sodium pump. All bacteria that failed to grow without the addition of NaCl possessed a primary Na pump. All bacteria that had no primary Na pump grew without additional NaCl. The primary Na pump seems to be involved in the Na requirement of marine bacteria, and this can be regarded as a criterion for the definition of marine bacteria. 相似文献
123.
Summary A new anionic high molecular weight polysaccharide, Methylan, was produced byMethylobacterium organophilum from methanol as a sole source of carbon and energy under the specific culture conditions. By GPC and light scattering, the molecular weight was determined to be 2–4×106 dalton and the distribution of molecular weight was very homogeneous. Methylan was composed of carbohydrate (80%), uronic acid (12%), protein (6%) and pyruvic acid (5%). The sugar composition of Methylan was identified as glucose, galactose and mannose with the approximate molar ratio of 232. Methylan solution showed a pseudoplastic non-Newtonian fluid property at the concentration above 0.05%. At the concentration of 1% Methylan solution, the consistency index was 18,000 centipoise which was almost 10 times higher than that of Xanthan and the flow behavior index was 0.15. 相似文献
124.
Ligninolytic properties of different white-rot fungi 总被引:3,自引:0,他引:3
Summary Seven white-rot fungi were examined for the production of ligninase, manganese peroxidase and laccase. All these enzymes were found inTrametes gibbosa andTrametes hirsuta. Only manganese peroxidase and laccase were produced byPycnoporus cinnabarinus,Coriolopsis polyzona,Stereum hirsutum,Dichomitus squalens andGanoderma valesiacum. All fungi decolorized Poly B-411 and Indulin AT plates with low-N medium. The differences in enzyme pattern indicate that different species of fungi may employ different modes of lignin metabolism. 相似文献
125.
G. H. Canullo R. Rodríguez‐kábana J. W. Kloepper 《Biocontrol Science and Technology》1992,2(2):159-169
The efficacy of 2‐furfuraldehyde for control of Sclerotium rolfsii was studied in laboratory and greenhouse experiments. Mycelial growth of the fungus was reduced proportionally with concentrations of 0.1–0.5 ml furfuraldehyde l‐1 agar medium, and viability of sclerotia diminished on exposure to 2‐furfuraldehyde vapours. Detectable populations of bacteria and fungi, including Trichoderma spp., were reduced significantly (9=0.05) when furfuraldehyde was added to the agar used for soil dilution plates of untreated soil. Repeated treatments of natural soil with the fumigant significantly increased populations of Trichoderma spp. and bacteria, but diminished numbers of actinomycetes. Increasing dosages applied to soil artificially infested with S. rolfsii caused a reduction of disease on lentil, Lens culinaris. Results indicate that the compound, when applied to field soil, changes the composition of soil microflora and has potential for integrated control of S. rolfsii. 相似文献
126.
Tracey C. Bourner Enrique Vargas‐Osuna Trevor Williams Candido Santiago‐Alvarez Jenny S. Cory 《Biocontrol Science and Technology》1992,2(4):315-326
Agrotis segetum nuclear polyhedrosis virus (AsNPV) and granulosis virus (AsGV), propagated in laboratory cultures of A. segetum in England and A. ipsilon in Spain, respectively, were applied to plots of maize plants at the one‐ to four‐leaf stage of growth. Plots were arranged in a 6 x 6 Latin square design and infested with second‐instar A. segetum larvae (the common cutworm). Each virus was applied in separate treatments by two application methods; as an aqueous spray containing 0.1% Agral as a wetting agent, and as a bran bait. The NPV was applied at a rate of 4 X 1012 polyhedra/ha, and the GV at 4 X 1013 granules/ha. Soil and plants were sampled for larvae on three occasions following virus treatment: 24 h, 4 days and 11 days. The larvae were reared on diet in the laboratory, until death or pupation, to examine the rate and level of viral infection. Infection data showed 87.5% and 91% NPV infection and 12.5% and 55% GV infection in spray and bait treatments, respectively, in larvae sampled 24 h after treatment. In larvae sampled 4 days after treatment, the results were 78% and 100% NPV infection, and 13% and 6% GV infection. A total of only six larvae were retrieved on day 11. In both treatments larvae infected with AsNPV died significantly more rapidly and at an earlier instar than those infected with AsGV, indicating that AsNPV appears to have better potential as a control agent for A. segetum. 相似文献
127.
V. M. Oh 《BMJ (Clinical research ed.)》1992,305(6860):1000
128.
Direct repeats flanking the Bacteroides transposon Tn4351 are insertion sequence elements. 总被引:11,自引:5,他引:6
下载免费PDF全文
![点击此处可从《Journal of bacteriology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The clindamycin-erythromycin resistance (Ccr Emr) region of the Bacteroides transposon Tn4351 is flanked by direct repeats. This study showed that the direct repeats are insertion sequence (IS) elements. Although both IS elements can mediate transfer of the chloramphenicol (Cmr) marker on pBR328 by cointegrate formation with the conjugal IncW plasmid R388, IS4351R-mediated transfer of Cmr occurred at a consistently lower frequency than did the transfer mediated by IS4351L. Analysis of plasmids from the resultant transconjugants revealed IS-mediated activities such as deletions, tandem duplication of IS4351L, and excision of IS4351R. 相似文献
129.
A carrier-supported mycelial growth of Penicillium chrysogenum was applied to penicillin fermentation system using celite as a support material. Hyphal growth through the pore matrices of the material showed strong anchorages and provided highly stable biofilm growth. With bioparticles developed in such a manner, both cell growth and penicillin production were observed to increase significantly compared to the conventional dispersed filamentous cultures. Maximum values of specific penicillin production rate were found to be constant regardless of the growth form. A three-phase fluidized-bed fermentor was designed and tested for penicillin production using the bioparticles. Two modes of operation, semicontinuous and repeated fed batch, of the fermentor were tried. It was noted that the overgrowth of free mycelia and the development of fluffy loose bioparticles caused poor mixing and made the fermentor operation quite difficult. Control of the bioparticle size and the extension of production phase were therefore considered important to maintain the reactor productivity at a desired level. From the results of repeated fed-batch operation it was found that the control of bioparticle size could be successfully achieved by phosphate-limiting culture condition. Penicillin production under this condition was also observed to be maintained at a high level (about 80% of the maximum) for at least 1 month. 相似文献
130.
Mycological survey of Korean cereals and production of mycotoxins by Fusarium isolates. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
U S Lee H S Jang T Tanaka N Toyasaki Y Sugiura Y J Oh C M Cho Y Ueno 《Applied microbiology》1986,52(6):1258-1260
The fungal species isolated from Korean cereals (barley, polished barley, wheat, rye, and malt) were Alternaria spp., Aspergillus spp., Chaetomium spp., Drechslera spp., Epicoccum sp., Fusarium spp., and Penicillium spp., etc. The number of Fusarium strains isolated was 36, and their ability to produce Fusarium mycotoxins on rice was tested. Nivalenol (NIV) was produced by Fusarium graminearum (7 of 9 isolates), Fusarium oxysporum (3 of 10 isolates), and Fusarium spp. (7 of 15 isolates). Of 15 isolates of Fusarium spp., 6 formed deoxynivalenol (DON). Fusarenon-X and 3-acetyl-DON were produced by most NIV- and DON-forming isolates, respectively. Zearalenone was produced by 3 isolates of F. graminearum, 1 isolate of Fusarium equiseti, and 11 isolates of Fusarium spp. T-2 toxin was not produced by any Fusarium isolates. The highest concentrations of mycotoxins produced by Fusarium isolates were 77.4 (NIV), 5.3 (DON), 138.3 (fusarenon-X), 40.6 (3-acetyl-DON), and 23.2 (zearalenone) micrograms/g. 相似文献